Illumination system and method for efficiently illuminating a pattern generator

ABSTRACT

An illumination method and system use a light source and illumination optics to illuminate a pattern generator. The illumination optics can include at least two devices. For example, if first and second diffractive and/or refractive devices are used, one can be a pupil defining element (PDE) and one can be a field defining element (FDE). In another example, a third diffractive or refractive element can be used to make light entering the illumination system uniform. When only two are used, the PDE forms one or more light beams having a defined profile. The FDE directs the one or more light beams having the defined profile, such that each directed beam substantially corresponds in size and shape to a desired illumination area(s) on the pattern generator. The directed beams are directed to impinge substantially only on the desired illumination area(s). Thus, using the PDE and the FDE increases optical efficiency of light impinging on the pattern generator and substantially reduces or eliminates stray light caused by light impinging on undesired areas of the pattern generator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 10/270,556,filed Oct. 16, 2002 now U.S. Pat. No. 6,775,069 entitled “AdvancedIllumination System for Use in Microlithogrpahy,” (published as U.S.Patent Application Publication No. 2003/0076679 A1 on Apr. 24, 2003),which claims benefit under 35 U.S.C. 119(e) to U.S. ProvisionalApplication No. 60/329,758, filed Oct. 18, 2001, which are bothincorporated herein by reference in their entireties.

This application is also a continuation-in-part of U.S. Ser. No.10/166,062, to Oskotsky et al., entitled “Advanced Illumination Systemfor Use in Microlithography,” filed Jun. 11, 2002 (now U.S. PatentApplication Publication No. 2003/0227609 A1), which is incorporated byreference herein in its entirety.

This application is related to U.S. Ser. No. 10/812,978, filed Mar. 31,2004 (1857.0700003), which is incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to an illuminating system and methodfor illuminating a pattern generator, and more particularly forilluminating a pattern generator in a lithography system.

2. Background Art

Pattern generators are used in many different environments to patternobjects or project patterns using light, for example, in lithographysystems, televisions, biomedical systems, biotechnology systems, etc.Typically, reticles (or masks), spatial light modulators (SLMs) orcontrast devices (hereinafter, both are referred to as SLMs), such asdigital mirror devices (DMDs), liquid crystal displays (LCDs), gratinglight valves (GLVs), or the like, or any other elements that include atransmissive and/or reflective pattern can be used as patterngenerators.

SLMs can include an active area having an n×m (wherein n and m areintegers greater than 1) array of active devices (or pixels) (e.g., anarray of mirrors on the DMD, an array of gratings on a GLV, or an arrayof reflective/transmissive devices on the LCD). Each active device isindividually controlled to move the active devices between ON and OFFthrough one or more discrete states. For example, if the active devicesare mirrors on the DMD, each of the mirrors is individually controlledto rotate or tilt the mirror to either binary or multiple positions. Asanother example, if the active devices are strips in a GLV, sets ofstrips can be bent or straight to allow reflection or diffraction ofincoming light beams.

It is to be appreciated that controlling the active devices in activeareas so that they are partially or fully ON or OFF is well know in theart, and not fully described here for brevity. Typically, apredetermined and previously stored algorithm based on a desiredexposure pattern is used to turn ON (or partially ON) and OFF the activedevices, as is known in the relevant arts.

FIGS. 1, 2, and 3 show conventional systems 100, 200, and 300,respectively, for illuminating a pattern generator, so that patternedlight is formed and directed from the pattern generator. As is known,the illumination optics, and optional pattern generator optics, caninclude one or more optical elements (e.g., lenses, mirrors, etc.). Inone arrangement, the illumination optics can include the patterngenerator optics. In another arrangement, the pattern generator opticscan be a separate element. A projection system would normally focuspatterned light from the pattern generator onto a substrate.

FIG. 4 shows a convention illumination field 400 that can result fromsystems 100, 200, and/or 300 for pattern generator 402 having desiredillumination areas 404. Each illumination area can be either an activearea of an SLM or a desired portion of a pattern on a reticle. Asdiscussed above, each active area will include the active devices. Ascan be seen, illumination field 400 is so large that it not onlyimpinges on desired illumination areas 404, but is larger than patterngenerator 402. Thus, a substantial amount, maybe up to about 80–90%, ofthe light may be wasted (i.e., not used during operation of system 100,200, and/or 300) because that amount of light does not impinge ondesired illumination areas 404.

One use for the pattern generator, or an array thereof, is in masklesslithography. Lithography is a process used to create features on thesurface of a substrate. Such substrates can include those used in themanufacture of flat panel displays (e.g., liquid crystal displays),circuit boards, various integrated circuits, and the like. A frequentlyused substrate for such applications is a semiconductor wafer or flatpanel display glass substrate. While this description is written interms of a semiconductor wafer for illustrative purposes, one skilled inthe art would recognize that this description also applies to othertypes of substrates known to those skilled in the art.

During lithography, a wafer, which is disposed on a wafer stage, isexposed to an image (e.g., a pattern) formed by the pattern generator,or array thereof. The image is projected onto the surface of the waferby exposure optics located within a lithography apparatus. Whileexposure optics are used in the case of photolithography, a differenttype of exposure apparatus can be used depending on the particularapplication. For example, an excimer laser, x-ray, ion, electron, orphoton lithography can each require a different exposure apparatus, asis known to those skilled in the art. The particular example ofphotolithography is discussed here for illustrative purposes only.

The projected image produces changes in the characteristics of a layer(e.g., photoresist) deposited on the surface of the wafer. These changescorrespond to features in the image projected onto the wafer duringexposure. Subsequent to exposure, the layer can be etched to produce apatterned layer. The pattern corresponds to the features projected ontothe wafer during exposure. This patterned layer is then used to removeor further process exposed portions of underlying structural layerswithin the wafer, such as conductive, semiconductive, or insulativelayers. This process is then repeated, together with other steps, untilthe desired features have been formed on the surface, or in variouslayers, of the wafer.

Step-and-scan technology works in conjunction with a projection opticssystem that has a narrow imaging slot. Rather than expose the entirewafer at one time with the image formed by the pattern generator,individual fields are scanned onto the wafer one at a time. This isaccomplished by moving the wafer and controlling active devices on thepattern generator, such that the imaging slot is moved across the fieldduring the scan. The wafer stage must then be stepped between fieldexposures to allow multiple copies of the pattern formed by the activedevices on the pattern generator to be exposed over the wafer surface.In this manner, the quality of the image projected onto the wafer ismaximized.

Desired illumination areas on a pattern of a reticle (or mask) or theactive area of the SLM are usually substantially smaller than a size ofa surface incorporating the desired illumination areas of the pattern orthe active area. For example, in an SLM, an active area may only be10–20% of the SLM surface, with the remaining surface area of the SLMbeing an inactive area, which can include packaging, circuitry, and thelike. Thus, a substantial amount of the light directed to the patterngenerator may not impinge on the desired illumination area of thepattern or the active area, but instead impinges on undesired areas ofthe pattern or the inactive areas, which can result in stray lightand/or wasted light. Some of the stray light can reach the surface ofthe substrate. The stray light reaching the surface of the substrate cancause errors in devices being fabricated on the substrate.

Therefore, what is needed is a system and method that increases opticalefficiency by directing light such that it substantially impinges ondesired illumination areas of a pattern generator and that reduces orsubstantially eliminates stray light caused from light impinging onundesired areas of the pattern generator.

BRIEF SUMMARY OF THE INVENTION

An embodiment of the present invention provides a system thatsubstantially increases optical efficiency and substantially reduces oreliminates the generation of stray light generated when illuminationlight impinges on undesired areas of a pattern generator. The systemincludes a light source, a pupil defining element (PDE), a fielddefining element (FDE), an optical system, and the pattern generator.The PDE and FDE can be diffractive or refractive devices. Light emittedfrom the light source is transmitted through the PDE and FDE to formshaped and directed beams that are directed onto one or more desiredillumination areas of the pattern generator and are directedsubstantially away from undesired areas of the pattern generator.

Other embodiments of the present invention include a method thatsubstantially increases optical efficiency and substantially reduces oreliminates the generation of stray light generated when illuminationlight interacts with a pattern generator (e.g., a reflective ortransmissive reticle or SLM). The method includes transmitting lightthrough a PDE and a FDE to form beams of light, directing the beams oflight using an optical system towards the pattern generator, andsubstantially illuminating only the desired illumination areas of thepattern generator and substantially no undesired areas of the patterngenerator, based on the transmitting and directing steps.

Further embodiments, features, and advantages of the present inventions,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIGS. 1, 2, and 3 show high-level block diagrams of systems forilluminating pattern generators.

FIG. 4 shows an array of pattern generator areas that need to beilluminated.

FIG. 5 shows an arrangement of illumination optics according to anembodiment of the present invention.

FIG. 6 shows a light path from a diffraction or refraction device to apattern generator according to an embodiment of the present invention.

FIG. 7 shows an illumination pattern on a pattern generator according toan embodiment of the present invention.

FIG. 8 shows an exemplary system using an illumination system accordingto an embodiment of the present invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers mayindicate identical or functionally similar elements. Additionally, theleft-most digit(s) of a reference number may identify the drawing inwhich the reference number first appears.

DETAILED DESCRIPTION OF THE INVENTION

Overview

While specific configurations and arrangements are discussed, it shouldbe understood that this is done for illustrative purposes only. A personskilled in the pertinent art will recognize that other configurationsand arrangements can be used without departing from the spirit and scopeof the present invention. It will be apparent to a person skilled in thepertinent art that this invention can also be employed in a variety ofother applications.

An embodiment of the present invention provides an illumination systemhaving a light source and illumination optics. The illumination systemis used to illuminate a pattern generator. The illumination opticsinclude at least two devices. For example, if first and seconddiffractive and/or refractive devices are used, one can be a pupildefining element (PDE) and one can be a field defining element (FDE). Inanother example, a third diffractive or refractive element can be usedto make light entering the illumination system uniform. When only twodevices are used, the PDE forms one or more light beams having a definedprofile. The FDE directs the one or more light beams having the definedprofile, such that each directed beam substantially corresponds in sizeand shape to a desired illumination area(s) on the pattern generator.The directed beams are directed to impinge substantially only on thedesired illumination area(s). Thus, using the PDE and the FDE increasesoptical efficiency of light impinging on the pattern generator andsubstantially reduces or eliminates stray light caused by lightimpinging on undesired areas of the pattern generator.

For the sake of brevity, a complete description of the operation andfunctionality of an SLM device (e.g., a DMD, a GLV, an LCD, etc.) beingused as the pattern generator is not described herein. For example, itis to be appreciated that controlling the active devices in active areasso that they are partially or fully ON or OFF is well know in the art,and not fully described here for brevity. Typically, a predetermined andpreviously stored algorithm based on a desired exposure pattern is usedto turn ON (or partially ON) and OFF the active devices, as is known inthe relevant arts.

It is also to be appreciated that illumination optics and patterngenerator optics can include one or more optical devices, for examplelenses, mirrors, and the like, or other light manipulating devices, aswould be known to a person of ordinary skill in the art upon readingthis description.

Illumination Optics

FIG. 5 shows an arrangement of elements in illumination optics 500according to an embodiment of the present invention. The illuminationoptics can be placed in any of systems 100, 200, or 300, or any othersystem used to illuminate a pattern generator. The illumination optics500 can be used to form shaped and directed beams, such thatsubstantially only desired illumination areas (e.g., pattern areas of areticle or active areas of an SLM device) are illuminated. This can beused to increase optical efficiency and decrease stray light.

A first device 502 (e.g., a pupil defining element (PDE)) is positionedin a pupil plane of illumination optics 500 and receives a light beam504 from a light source (not shown, but similar to those shown in FIGS.1, 2, or 3).

PDE 502 can comprise a refractive (e.g., lens array, etc.) ordiffractive (e.g., diffraction grating, etc.) optical element. PDE 502can be used to shape light beam 504 as it is transmitted therethrough.For example, PDE 502 can be used to define a light beam profile for oneor more light beams 506. For example, PDE 502 can form conventional,dipole, quadrapole, etc. profiles for beam(s) 506.

An optical device 507 (e.g., one or more optical elements) directsbeam(s) 506′ onto a second device 508 (e.g., a field defining element(FDE)). FDE 508 can be a refractive (e.g., a lens array, etc.) ordiffractive (e.g., diffraction grating, etc.) optical element, which ispositioned at a field plane of illumination optics 500. FDE 508 can beused to form one or more light beams 510 that maintain a shape ofbeam(s) 506′, but are directed to specific areas of a pattern generator(not shown) via optical device 512.

Although PDE 502 and FDE 508 are shown in a particular order inillumination optics 500, it is to be appreciated their order in theillumination path can be reversed, as is contemplated within the scopeof the present invention.

It is to be appreciated that first and second diffractive devices 502and 508, respectively, can include more than one diffractive orrefractive optical element. For example, in one embodiment usingdiffractive optical elements, first diffractive device 502 can alsoinclude a uniform beam profiling (UBP) diffractive optical elementpositioned before the PDE. In this embodiment, the UBP generates auniform beam profile from light beam 504.

Another exemplary optical system is shown in FIG. 2 a of U.S. Ser. No.10/270,556 (U.S. Patent Application Publication 2003/0076679 A1 (“the'679 PPA)), which is incorporated by reference herein in its entirety.The '679 PPA shows an optical system 200 that can be used to shape anddirect light.

System 200 in FIG. 2 a of the '679 PPA includes a first diffractivearray or field array 210, a second diffractive array or pupil array 212,and a condenser system 220 placed in an optical path along an opticalaxis 209 between first diffractive array 210 and second diffractivearray 212. First diffractive array 210 can be used to provide spatialand temporal coherence treatment for conditioned light 103 enteringillumination system 200. Second diffractive array 212 can act as a pupiland can change a magnitude of a light. Also, FIGS. 5 a, 5 b, 6 a, and 6b of the '679 PPA, and the description thereof, show exemplarydiffraction devices that can be used for first and second diffractivearrays 210 and 212.

Illumination optics 500 (or 200 in the '679 PPA) can be configured sothat PDE 502 and/or FDE 508 (or PDE 210 and FDE 212 in the '670 PPA) areeasily replaced (swapped) by other PDEs and FDEs. This can allow forillumination optics 500 (or system 200 in the '679 PPA) to be flexibleenough to produce any desired number, position, and/or size of directedbeams 510, as is appropriate for a particular desired illumination areaon the pattern generator. For example, the pattern generator can includea plurality of SLMs and only a predetermined set of the plurality ofSLMs form the desired illumination areas. In this case, a specific PDE502 and FDE 508 can be inserted into illumination optics 500 to producethe desired pattern. As another example, the pattern generator caninclude one or more SLMs each having varying sized active devices and/oractive areas. In this case, a specific PDE 502 and FDE 508 can beinserted into illumination optics 500 to produce the desired pattern. Inother examples, the interchangeability of PDEs and FDEs can allow asystem including illumination optics 500 to switch between high and lowresolution modes, to adjust throughput requirements, or the like.

Exemplary Light Path through the Illumination Optics

FIG. 6 shows a portion of a light path through illumination optics 500of FIG. 5 according to an embodiment of the present invention. It is tobe appreciated a similar light path can be formed through system 200 ofthe '679 PPA.

Light beam 506′ impinges FDE 508 to form beams 510-n. It is to beappreciated that a number of beams 510 in FIG. 6 is for illustrativepurposes. If pattern generator 602 included more or less desiredillumination areas 606 then the number of beams 510 would respectivelyreflect that number. If FDE 508 is a diffraction grating, beams 510 canbe desired orders of diffracted beams.

Beams 510 impinge on optical device 512 at areas 604-n. Directed beams510′-n exit optical device 512 and form an illumination spots 608 onrespective desired illumination areas 606 of pattern generator 602.Therefore, through the use of illumination optics 500, light 502 fromthe light source is shaped and directed so that each illumination spot608 covers only a small portion of a surface 610 and all of desiredillumination areas 606, which is best shown in FIG. 7.

FIG. 7 shows illumination areas 608. Using FDE 508 and optic 512,illumination spots 608 impinge substantially only on desiredillumination areas 606, while only covering a small (desired) portion ofsurface 610. In the example using an SLM for pattern generator 602,using illumination optics 500 of the present invention can increaseillumination efficiency up to around the 80–90% range.

Therefore, through use of illumination optics 500 (or system 200 in the'679 PPA) an increase in an amount of light intensity at each desiredillumination area 606 can result without a need to increase the power ofthe light source. Illumination optics 500 (or system 200 in the '679PPA) can further decrease or substantially eliminate stray light fromsurface 610, which decreases or substantially eliminates errors onfabricated devices caused by the stray light.

It is to be appreciated that, although illumination spots 608 are shownas certain shapes, the illumination spots 608 can be any shape. Theshape, as discussed above, can be based on FDE 508.

Exemplary Application of the Illumination System

One exemplary application that can use illumination system 500 (orsystem 200 in the '679 PPA) and pattern generator 602 can be a masklesslithography system 800, as described below. However, it is to beappreciated that other systems, such as those described above, can alsoemploy illumination system 500 to illuminate pattern generator 602.

FIG. 8 shows an exemplary lithography system 800 (e.g., a reticle ormaskless lithography system) that includes illumination optics 500 andprojection optics 850 according to an embodiment of the presentinvention. Light 504 from a light source (not shown) is shaped using PDE502 to form shaped beams 506. Shaped beams 506 are focused onto FDE 508using optical device 507 (e.g., a converging lens, or the like).Directed beams 510 are formed from FDE 508 and are focused onto desiredillumination areas 606 of pattern generator 602 using optical device 512(e.g., a converging lens, or the like). Reflected light beams 852 aredirected using an optical device 854 as beams 852′ through an aperture856. The light beams 852′ are then focused using optical device 858 ontoa substrate 860 (e.g., a wafer, flat panel display, or any object thatcan retain a received pattern) to pattern a photosensitive surface ofsubstrate 860.

It is to be appreciated that although a reflective pattern generator 602is shown, a transmissive pattern generator can also be used, as would beapparent to one of ordinary skill in the art upon reading thisdescription.

In one embodiments, uniformity of illumination within a patterngenerator and between pattern generators in an array of patterngenerators can be set using pattern generator calibration systems andmethods.

In another embodiment, an FDE can be configured to balance relative dosefrom pattern generator to pattern generator in an array. For example, aseries of filters (e.g., neutral density filters) down stream of the FDEcan be used to balance relative dose from one pattern generator toanother pattern generator.

In an embodiment performing stitching of pattern generator images, arollof profile may be required. In one example, the rollof profile isgenerated with an FDE. In another example, the rollof profile isgenerated prior to the FDE and the FDE is used to reproduce the rollofprofile.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

1. A system comprising a light source; a pupil defining element (PDE); afield defining element (FDE); an optical system; and a patterngenerator, wherein light emitted from said light source is transmittedthrough said PDE, said FDE, and said optical system to form illuminationspots that substantially impinge only on desired illumination areas ofthe pattern generator and are substantially directed away from undesiredareas of said pattern generator.
 2. The system of claim 1, wherein saidFDE is positioned closer to said pattern generator than said PDE.
 3. Thesystem of claim 1, wherein said PDE is positioned closer to said patterngenerator device than said FDE.
 4. The system of claim 1, wherein saidFDE and PDE are refractive devices.
 5. The system of claim 1, whereinsaid FDE and said PDE are diffractive devices.
 6. The system of claim 1,wherein said optical system comprises: a first optical elementpositioned after FDE; and a second optical element positioned after saidPDE.
 7. The system of claim 1, wherein said pattern generator comprisesone or more reflective pattern generating devices.
 8. The system ofclaim 1, wherein said pattern generator comprises one or more liquidcrystal display (LCD) devices.
 9. The system of claim 1, wherein saidpattern generator comprises one or more digital mirror devices (DMD).10. The system of claim 1, wherein said pattern generator comprises oneor more grating light valve devices.
 11. The system of claim 1, whereinsaid pattern generator comprises one or more reticles.
 12. The system ofclaim 1, wherein said pattern generator comprises one or moretransmissive pattern generator devices.
 13. The system of claim 1,wherein said pattern generator comprises one or more spatial lightmodulator (SLM) devices.
 14. The system of claim 1, further comprising:a light uniformity producing element positioned after the light source.15. The system of claim 14, wherein the light uniformity producingelement is one of a diffractive element and a refractive element. 16.The system of claim 1, wherein the PDE comprises one or more PDEs. 17.The system of claim 1, wherein the FDE comprises one or more FDEs.
 18. Amethod comprising: transmitting light through a PDE and a FDE to formbeams of light; directing said beams of light towards a patterngenerator; and illuminating substantially only desired illuminationareas and avoiding undesired areas of said pattern generator based onsaid transmitting and directing steps.
 19. The method of claim 18,wherein said transmitting step comprises forming diffracted light assaid beams of light using said FDE and said PDE.
 20. The method of claim18, further comprising: patterning a substrate with light that reflectsfrom the desired illumination areas.
 21. The method of claim 18, furthercomprising: patterning a substrate with light that transmits through thedesired illumination areas.
 22. The method of claim 18, furthercomprising using one of a reticle or a contrast device as the patterngenerator.
 23. The method of claim 18, further comprising: using auniform beam profiler to produce light having a uniform beam profile asthe light is transmitted through the PDE and the FDE.